This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. We developed a double differential method to analyze the near-infrared spectra of regions of the breast with tumors. We show that the near-infrared (650-1000nm) spectra of breasts with tumors have characteristic absorption bands in the lipid fingerprint region that are unaccounted for in conventional spectral models. These spectral components do not appear in the normal breast of the same patient or in regions of the diseased breast away of the tumor. These spectral components originate from lipids that are present in tumors either in different abundance than in the normal breast or new lipid components that are caused by the different metabolism in tumors. Furthermore, the water band in the 980-1000 nm region also shows distinct variations in the tumor region compared to the normal breast. By combining the information in the lipid and water region, we constructed an index that is characteristic of the tumor region (100% specificity and 93% sensitivity for the 17 patients investigated) and has the potential to distinguish benign form malignant tumors on the basis of the lipid composition and /or bound water. This index can be combined with previously described indexes based in the amount of water, lipids and hemoglobin to further improve the diagnostic power of optical spectral methods. Surprisingly, the size of the tumor (range 4-70 mm) does not correlate with the value of this index, providing similar sensitivity for small and larger tumors.